The Invisible War, from Kirby Dick, the Oscar-nominated director of This Film Is Not Yet Rated, screened at the Los Angeles film festival over the weekend and is not due to arrive in cinemas elsewhere in the US until Friday 22 June. Even so, the film-makers have embarked on a determined effort to screen the movie for members of Congress and staff at the department of defence and the Pentagon.

Among other harrowing stories, the film details the experiences of Kori Cioca, who was serving in the US coast guard in December 2005 when she was raped by a commanding officer in an assault which broke her jaw. When she sought to move forward with her case, her own commanding officer told her she would face court martial for lying if she pursued the issue. Her assailant, who admitted to the assault while denying that rape was part of it, was "punished" by being restricted to the base for 30 days and docked some pay. Cioca now has post-traumatic-stress-disorder, along with nerve damage to her face.

She is fighting the Veterans Administration (VA) to receive approval for surgery she urgently needs and has also become a plaintiff in a class action civil suit against the department of defence.

Dick told The Wrap that Panetta saw the film in April, and almost immediately called a press conference to announce changes in policy towards the prosecution of rape in the military. The film-makers discovered their coup when the secretary of defence ran into one of the film's executive producers, Jennifer Siebel Newsom, at a White House dinner. "He thanked her for making the film, said he was very moved by it, and told her that he had held the press conference in part because the film had made such an impact on him," Dick said.

Previously, US military policy was to allow unit commanders to oversee investigation and prosecution of reported assaults, a position which critics said often placed power in the hands of men who worked with, and were close friends of, the accused. The responsibility has now been moved higher up the chain of command to the level of US army colonel or navy captain, which the film-makers believe is a useful stepping stone towards the goal of wiping out the estimated 19,000 assaults that take place in the US military each year.

The move will not solve the problem overnight, however. "By moving the decision up but leaving it in the chain of command, a lot of the problems that you get at the unit commander level still exist," Dick said. "They might be somewhat mitigated, but they're still definitely there in terms of conflict of interest. The decision absolutely must be moved outside the chain of command, to an independent arbiter who has no relationship to the perpetrator or to the victim."

A number of bills are currently before Congress seeking further changes to the law. Democratic congresswoman Jackie Speier hopes to introduce the Sexual Assault Training Oversight and Prevention Act, which would move the decision to investigate and prosecute completely out of the military and put it under civilian control.

In the meantime, the film-makers can point to another coup as evidence that their call for change is being heard by the powers that be. Major general Mary Kay Hertog, who headed the military's sexual assault prevention and response office (SAPRO), and whose comments in the film position her as a defender of the status quo, has been removed from her position. "I'm not going to gloat about it," producer Amy Ziering told The Wrap. "But the timing is interesting."

• This article was amended on 20 June 2012 because the original described Jackie Speier as a Republican congressman. Speier is a Democratic congresswoman. This has been corrected.